"I will stake my mayorship on the results of Wednesday's referendum and take full responsibility for them," he told a press conference in City Hall.

"If my decision today can sow the seeds to bear the fruits of sustainable welfare and true democracy in this country, I have no regrets even if (I) fade into the mists of history," he said.

The mayor stressed that the referendum must be used as an opportunity to demonstrate the will of the citizens.

The vote asks citizens to choose between the opposition-led program of free school lunch for all students and one that prioritizes those in most need. Oh has argued that providing free lunch to all students is a populist policy weighing on government finances, while opposition parties claim poor students receiving free lunch could be stigmatized at school.

The ballot will be counted only if one-third of the city's 800,000 eligible voters participate in the vote, the first such poll for Seoul. Opposition parties are encouraging citizens to boycott the vote to nullify the referendum aimed at stopping the free lunch program.

Oh's announcement comes days after the mayor said he will not run in next year's presidential race, rejecting speculation that he is using the referendum to boost his political fortunes ahead of the election.